1. Technical Field
The present disclosure generally relates to generating audible signals, and more particularly, to systems, methods and physical structures for efficiently generating audible signals by or in connection with hazard detectors such as smoke detectors and carbon monoxide detectors.
2. Description of the Related Art
A variety of commercially available detector/alert devices exist for alerting individuals of the presence of smoke, heat, and/or carbon monoxide. These devices are typically designed to be mounted to the ceiling in various rooms of a house or other building, and are ordinarily powered by the building's AC power lines with battery backup. The audible alert signals generated by such devices are governed by various standards and regulations such as Underwriters Laboratories (UL) 217 (“The Standard of Safety for Single and Multiple Station Smoke Alarms”), UL 464 (“The Standard of Safety for Audible Signal Appliances”), UL 1971 (“The Standard for Signaling Devices for the Hearing Impaired”), and UL 2034 (“The Standard of Safety for Single and Multiple Station Carbon Monoxide Alarms”).
According to these and other standards, typical smoke, fire, and carbon monoxide detectors produce a 3100-3200 Hz pure tone alert signal with the intensity (or power) of 45 to 120 dB (A-weighted for human hearing). The alert signals typically have either a repeated temporal-three (T3) pattern (three beeps followed by a pause) or a repeated temporal-four (T4) pattern (four beeps followed by a pause), and are generated using a piezoelectric device. Studies have shown that the 3100-3200 Hz alert signals generated by existing detector/alert devices are sometimes inadequate for alerting certain classes of individuals. These include children, heavy sleepers, and the hearing impaired.
Various fire alarm signal studies commissioned by the U.S. Fire Administration and Fire Protection Research Foundation have demonstrated that a 520 Hz square-wave signal is more effective at waking children, heavy sleepers and people with hearing loss than current alarms that use a 3100-3200 Hz pure tone alert signal. Accordingly, new regulations may soon require the use of a relatively low-frequency (520 Hz) square-wave alert signal, or a signal with similar characteristics, for fire alarms installed in residential bedrooms of those with mild to severe hearing loss, and in commercial sleeping rooms.